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How to Complete an HST Charge Pressure Test on Your Yanmar Tractor

We want to help you complete an HST charge pressure test on your Yanmar tractor.

If you do not feel that you understand these steps, or can perform them safely, consult your tractor dealer or local mechanic. Also always consult your tractor owner’s manual for model-specific information.

The purpose of this test is to make sure that the hydrostatic pump is producing sufficient pressure to operate the hydrostatic motor pump.

Time to get started.


1 Remove the rear right wheel.

  • Make sure to use a suitable lifting device.

  • Make sure to support the rear axle with suitable jack stands.

  • Make sure that the range gear lever is in the N (neutral) position. (SA324/424 only.)

2. To complete this task you will need to purchase the following equipment and tools:

  • Adapter fitting (3/8")

  • Hydraulic pressure gauge

  • Hose with coupler

3. Warm up the hydraulic oil.

  • Start the engine.

  • Operate the hydraulic system to circulate and heat up the hydraulic oil.

  • The hydraulic oil must be heated up to the normal operating temperature of 140 °F (60 °C).

  • Check for oil leaks.

  • Shut off the engine.

IMPORTANT: Avoid damage. Do not overheat the hydraulic oil.

CAUTION: Avoid injury. Escaping fluid under pressure can penetrate the skin causing serious injury.

4. Hydrostatic transmission (HST) charge pressure test.

  • Remove the test port plug from the charge pressure test port (A, Fig.1) in the center plate.

  • Install the following to the charge pressure test port.

- Adapter fitting

- Hydraulic pressure gauge (B, Fig.1)

- Hose with coupler

  • Perform the following procedure.

- Start the engine

- Run the engine at 3200 rpm

- Read the charge pressure on the hydraulic pressure gauge - pressure reading must be 71.05 - 114.55 psi (0.49 - 0.79 MPa)

- Shut off the engine

  • Remove the following from the charge pressure test port.

- Hose with coupler

- Hydraulic pressure gauge

- Adapter fitting

  • Install the test port plug.

  • Check for oil leaks on the hydrostatic transmission (HST).

  • After the test, apply the sealing tape to the plug to tighten the plug to: 5.8 to 8.7 fl·lbs (7.8 to 11.8 N·m)

A - Charge pressure test port

B - Hydraulic pressure gauge

WARNING: The charge pressure test should not exceed 30 seconds to avoid overheating of the hydraulic oil.

NOTE: When the charge pressure test reading does not conform to the required specification --- remove and repair the hydrostatic transmission (HST) pump and motor.

If you need any further help or have any questions about HST tests, tractors, or anything else, please contact your dealer, local mechanic, or call us at 602-734-9944. Please ask about our current new and used tractor supply.

Tractor Ranch - #1 Tractor Dealer in Arizona. We sell and service most major brands of tractors including Yanmar, Kubota, John Deere, TYM, Mahindra, Kioti, Case, New Holland, Massey Ferguson, Ford, Deutz, Case IH, Farmall, International Harvester, Branson Tractors, LS, Shibura, Claas Tractor, McCormick Tractors, Valtra, Solis, YTO, Montana, and Nortrac.

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